Existing transmitters must be taken out of service and powered down before any field upgrades or repairs can be made to avoid violating IS (Intrinsically Safe) operating procedures. This process typically requires special permits, scheduling, and downtime for users.
In general, intrinsic safety (IS) is a protection technique for safe operation of electronic equipment in explosive atmospheres and under irregular operating conditions. The concept was developed for safe operation of process control instrumentation in hazardous areas such as, for example, North Sea gas platforms. As a discipline, it is an application of inherent safety in instrumentation.
The theory behind intrinsic safety is to ensure that the available electrical and thermal energy in the system is always low enough that ignition of the hazardous atmosphere cannot occur. This is achieved by ensuring that only low voltages and currents enter the hazardous area, and that Zener safety barriers protect all electric supply and signal wires. Sometimes an alternative type of barrier known as a galvanic isolation barrier may be used.
In normal uses, electrical equipment often creates internal tiny sparks in switches, motor brushes, connectors, and in other places. Such sparks can ignite flammable substances present in air. A device termed intrinsically safe is designed to not contain any components that produce sparks or which can hold enough energy to produce a spark of sufficient energy to cause an ignition. For example, during marine transfer operations when flammable products are transferred between the marine terminal and tanker ships or barges, two-way radio communication needs to be constantly maintained in case the transfer needs to stop for unforeseen reasons such as a spill. The United States Coast Guard requires that the two-way radio must be certified as intrinsically safe.
Another aspect of intrinsic safety is controlling abnormal small component temperatures. Under certain fault conditions (such as an internal short inside a semiconductor device), the temperature of a component case can rise to a much higher level than in normal use. Safeguards, such as current limiting by resistors and fuses, must be employed to ensure that in no case can a component reach a temperature that could cause auto ignition of a combustible atmosphere.
No single field device or wiring is intrinsically safe by itself (except for battery-operated, self contained devices), but is intrinsically safe only when employed in a properly designed IS system. All systems are provided with detailed instructions with the proper instructions to ensure safe use.
Intrinsic safety is a requirement that may be applicable to devices that are being operated in areas with flammable gases or fuels. It means that the device is incapable of igniting those gases. In short, an intrinsically safe piece of equipment won't ignite flammable gases. ISA-RP12-6, for example, defines intrinsically safe equipment as “equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration.”
Many ultra ruggedized mobile computers will include intrinsically safe (IS) specifications or approval ratings. Understanding IS approval ratings can be a difficult proposition for even the most informed user. Intrinsically safe areas are hazardous environments where flammable gases, vapors, and liquids are stored and manufactured. These areas are prevalent in many of today's manufacturing facilities including chemical plants, paint manufacturers, oil refineries, textile mills, etc.
Each designated hazardous environment has specific certification requirements for all equipment used in the IS area. Intrinsically safe equipment must carry a label, which specifies the exact IS rating for the equipment and the name of the NRTL (Nationally Recognized Testing Laboratory) who tested it. Testing laboratories have very stringent certification requirements that vary according to the level of IS approval desired. Therefore, each intrinsically safe device is certified for different levels of IS approval and can only be used in specific hazardous environments. The bottom line is that close attention must be given to the specific IS approval certification for each individual piece of equipment. Just because a device has an IS rating does not mean that the device can be used in any IS area.
IS approval certifications are made up of multiple classes, groups, and divisions that correspond to the specific hazardous environment a device is approved to operate in. Each class consists of two divisions and certain classes have multiple groups. For example, Class I includes flammable gases, Class II includes flammable dust, and Class III includes flammable fibers. Each class has two divisions. Division 1 includes environments where explosive material is present in the air at all times. Division 2 includes environments where explosive material is stored in sealed containers, and explosive material is only present for short time intervals (when a failure occurs or during maintenance). Also, Classes I and II are broken down into groups that correspond to the explosive properties of each specific material. For example, Group A includes Acetylene and Group E includes aluminum dust. In addition, IS approval ratings differ significantly from country to country. A device that is IS certified for use in the U.S. may not be certified, for example, in Europe.
A transmitter can be coupled to process equipment to assist in detecting and transmitting process variable data such as, for example, data that is indicative of pressure, temperature, flow, etc. In a typical configuration, a transmitter can be located at a remote location and sensed process variables can be transmitted to a receiving device or system such as, for example, a control room in an industrial setting. Various techniques can be employed to transmit process variables including wired and/or wireless communications. Pressure transmitters, for example, are utilized in industrial process control environments to measure the pressure of a fluid (e.g., gas, liquids and their combination) with respect to the particular process. Pressure transmitters can also be employed to assist in the measurement and transmission pressure data such as, for example, differential, absolute or gauge pressures.
Conventional transmitters must be periodically taken out of service and powered down before any field upgrades or repairs can be made, in order to avoid violating intrinsically safe operating procedures. Such an approach requires special permits, scheduling, and downtime. Unfortunately, making improvements and modifications to existing transmitter systems is a highly complex process as improvements and modifications made to, for example, a communication board, may encroach on the other electronics on the same board of the transmitter. Additionally, the transmitter must be turned off before removing the electronics on the same board for repair. Such an approach creates discontinuity in the operation of the transmitter system and also requires special permits, scheduling, and downtime.
Based on the foregoing, it is believed that a need exists for an improved intrinsically safe serviceable transmitter apparatus and method, as described in greater detail herein.